Hydrogen fluoride alkylation utilizing a rectification zone

ABSTRACT

An improved process for increasing the yield and octane number of alkylated hydrocarbons produced from isoparaffin-olefin admixtures wherein a rectification zone removes hydrogen fluoride from recycle isoparaffin. Removal of hydrogen fluoride prevents detrimental side reactions which would occur upon the mixing of recycle isoparaffin with fresh olefin were hydrogen fluoride allowed to remain in the recycle isoparaffin. Higher octane alkylate results from elimination of these side reactions. The rectification zone also serves to reduce the load on the separation zone, enabling the processing of higher rates of feed stock than would be possible without the rectification zone.

United States Patent 9] Anderson July 8,1975

[ HYDROGEN FLUORIDE ALKYLATION UTILIZING A RECTIFICATION ZONE [75] lnventor: Robert F. Anderson, La Grange Park, Ill.

22 Filed: Dec. 26, 1973 21 Appl. No.: 428,148

3,767,726 10/1973 Hutson, Jr. et a1. 260/683.48 3,775,510 11/1973 Hutson, Jr. et a1. 260/683.48 3,796,769 3/1974 Ward 260/683.48

Primary Examiner-Delbert E. Gantz Assistant Examiner-G. J. Crasanakis Attorney, Agent, or FirmJames R. Hoatson, Jr.; Robert W. Erickson; William H. Page, 11

[5 7 ABSTRACT An improved process for increasing the yield and octane number of alkylated hydrocarbons produced from isoparaffin-olefin admixtures wherein a rectification zone removes hydrogen fluoride from recycle isoparaffin. Removal of hydrogen fluoride prevents detrimental side reactions which would occur upon the mixing of recycle isoparaffin with fresh olefin were hydrogen fluoride allowed to remain in the recycle isoparaffin. Higher octane alkylate results from elimination of these side reactions. The rectification zone also serves to reduce the load on the separation zone, enabling the processing of higher rates of feed stock than would be possible without the rectification zone.

8 Claims, 1 Drawing Figure Liau/fied Hydrocarbon Vapor To Fractional/on [l0 2 5 Separation Zone\ /o fioclificalian I Zone 1 [3 Reaction Zone Hydrocarbon 2 Liquid To I f9 Treafing Acid CaIa/ys/ 2 /4 l Olefin Isa-paraffin 2 Feed /2 J lso-paraf/in J I Recycle Isa-paraffm 2 Al/ry/are Producl HYDROGEN FLUORIDE ALKYLATION UTILIZING A RECTIFICATION ZONE BACKGROUND OF THE INVENTION 1. Field of the Invention The field of art to which this invention pertains is hydrocarbon processing. It particularly relates to an im proved process for the production of an isoparaffinolefin alkylation product through hydrogen fluoride catalysis.

2. Prior Art Production of higher molecular weight isoparaffins, having valuable antiknock properties as motor fuel, is of considerable importance in the petroleum refining industry. Furthermore, the growth of the synthetic fibers and plastics industries has increased consumption of aromatic hydrocarbons such that less are available for use as high octane motor fuel blending components. Thus, a demand for higher molecular weight isoparaffins as blending agents for fuels has materialized. Concatenating with this demand for higher octane blending components is a demand for greater quantities of the blending components themselves due to the incessant increase in world gasoline consumption.

A convenient source of such higher molecular weight isoparaffins is the catalytic alkylation of lower boiling isoparaffinic hydrocarbons, such as isobutane, with olefinic hydrocarbons, such as propene and butenes. It is well known in the art that catalytic alkylation using acid catalysts, such as hydrofluoric acid, has become an important tool for preparing alkylated hydrocarbons. However, there is an inherent feature of conventional designs of hydrogen fluoride-catalyzed alkylation process units which contributes to lower octane number products. Unreacted isoparaffins leaving the reaction zone of an alkylation process are recycled and mixed with fresh feed to provide, within the reaction zone, an excess of isoparaffinic components. Before entry again into the reaction zone, the recycle isoparaffins must be thoroughly mixed with other feed components such as fresh isoparaffins and fresh olefins. Due to the design of conventional alkylation processs units the recycle isoparaffin contains hydrogen fluoride, and this hydrogen fluoride catalyzes undesirable reactions which occur upon mixing of fresh olefins with the recycle isoparaffins, These undesirable reactions produce contaminants which remain in the final alkylate product and lower its quality. My invention solves this prior art problem by preventing these undesirable reactions from occurring.

Increased demand for high molecular weight isoparaffins has made necessary an increase in alkylate production capacity. Not infrequently, petroleum refiners build new alkylation process units similar to their original ones for the purpose of increasing alkylate production. In doing so they go to great expense, whereas in many of these instances the required incremental increase in unit capacity could have been achieved by the addition of a piece of equipment to the existing unit which would have served to eliminate the restriction to higher capacity. It has been found in many cases that the capacity limiting restriction in hydrogen fluoridecatalyzed alkylation process units is the separation zone, where the recycle isoparaffin is separated from the alkylate product. The improvement of my invention provides a method of increasing unit capacity by reducing the load on the separation zone while at the same time increasing the octane number of the alkylate produced.

BRIEF SUMMARY OF THE INVENTION My invention involves an improvement in quality of the alkylate product and an increase in the capacity of a hydrogen fluoride-catalyzed isoparaffin-olefin alkylation process unit. A rectification zone is employed between the mixing-settling zone and the separation zone of the process. This rectification zone removes hydrogen fluoride from the hydrocarbon effluent of the mixing-settling zone and provides a part of the recycle isoparaffin necessary to the process. As a result, the separation zone feed is substantially free of hydrogen fluoride, and recycle isoparaffin produced by the separation zone is substantially hydrogen fluoride-free. By furnishing a part of the recycle isoparaffin, the rectification zone lowers the duty of the separation zone of the process.

OBJECTS AND EMBODIMENTS It is an object of the present invention to provide an improved process for conducting an isoparaffin-olefin alkylation. It is a further object of this invention to provide an improved process for the hydrogen fluoride catalyzed alkylation of an isoparaffin with an olefin. A still further object of my invention is to provide a method for increasing the octane number of alkylate produced by alkylation of isoparaffins with olefins. Another object of the present invention is to provide a method of increasing the capacity of existing hydrogen fluoridecatalyzed alkylation process units.

In one embodiment my invention affords, in an alkylation process wherein: (a) a feed comprising an olefinacting hydrocarbon and an alkylatable hydrocarbon is contacted with hydrogen fluoride alkylation catalyst at alkylation reaction conditions in a reaction zone; (b) a reaction zone effluent is separated into a hydrogen fluoride phase and a hydrocarbon phase containing hydrogen fluoride; (c) the hydrogen fluoride phase is returned to said reaction zone; ((1) the hydrocarbon phase containing hydrogen fluoride is passed to a separation zone; (e) at least a portion of unreacted alkylatable hydrocarbons is withdrawn from said separation zone and mixed with said feed prior to the introduction thereof into said reaction zone; and, (f) an alkylate product is withdrawn from said separation zone; The improvement which comprises introducing said hydrocarbon phase into a rectification zone, therein removing a portion of the hydrogen fluoride, withdrawing an alkylate-containing stream from said rectification zone and passing said alkylate-containing stream to said separation zone.

BRIEF DESCRIPTION OF Tl-IE DRAWING The attached drawing illustrates a particular embodiment of the present invention. Only such details are included as are necessary for a clear understanding of my invention, and no intention is thereby made to unduly limit its scope. Certain items necessary to the operation of the process of this invention but unnecessary to its understanding, such as certain process streams, valves, pumps, instrumentation and other equipment, have been omitted for the sake of clarity.

Referring now to the drawing, an alkylation feed stream enters the process of this invention in conduit 1 and is premixed therein with recycle isoparaffin from conduit 2. This feed-recycle isoparaffin admixture then passes to reaction zone 4 where contact is effected with an acid catalyst. Reaction zone effluent, including acid catalyst, alkylated hydrocarbons and unreacted hydrocarbons, exits the reaction zone in conduit 5 and passes to mixing-settling zone 6, where mixing and further reaction take place, and, subsequently, the reaction zone effluent is settled and separatd into an acid phase and a hydrocarbon phase. The acid phase leaves mixingsettling zone 6 in conduit 3 and returns to reaction zone 4. The hydrocarbon phase from mixing-settling zone 6 exits in conduit 7 and passes to rectification zone 8. Rectification zone. 8 is maintained under conditions selected to provide a first stream essentially free of hydrogen fluoride, a second stream essentially hydrogen fluoride-free, a stream comprising hydrogen fluoride and a liquefied hydrocarbon vapor stream. A liquefied hydrocarbon vapor is a normally vaporous hydrocarbon which has been transformed from the vapor to the liquid state. The first hydrogen fluoride-free stream comprises alkylated hydrocarbons and unreacted hydrocarbons and exits rectification zone 8 in conduit 9, passing to separation zone 10. The second hydrogen fluoride-free stream, comprising isoparaffins, exits rectification zone 8 in conduit 12 and passes to conduit 2, intermixing therein with contents of conduit 2. The hydrogen fluoride stream from rectification zone 8 exits in conduit 10 and passes to conduit 3, intercombining therein with the hydrogen fluoride stream from mixingsettling zone 6. Liquefied hydrocarbon vapor from rectification zone 8 exits in conduit 11 and passes to downstream fractionation facilities. The first hydrogen fluoride-free stream from rectification zone 8 passes in conduit 9 to separation zone 10'. Separation zone 10' is operated at conditions selected to provide an alkylate product stream, a hydrocarbon liquid stream and a recycle isoparaffin stream. The alkylate product stream exits separation zone 10 in conduit 14. Hydrocarbon liquid leaves separation zone 10' in conduit 13. Recycle isoparaffin exits separation zone 10 in conduit 2 and passes to conduit 1, intermixing therein, with feed to the reaction zone. It should be noted that the recycle isoparaffin in conduit 2, composed of isoparaffin from rectification zone 8 and isoparaffin from separation zone 10, which intermixes with the olefin-isoparaffin feed in conduit 1 is essentially hydrogen fluoride-free.

Feed to an alkylation process unit commonly contains, as well as the olefin and isoparaffin components, normal paraffins of carbon content substantially equal to that of the olefin and isoparaffin components. Hence, a feed comprising propene and butene as the olefinic components and isobutane as the isoparaffinic one will ordinarily contain at least some propane and normal butane. The propane and butane exit and process unit in the hereinbefore described liquefied hydrocarbon vapor stream aand in the hydrocarbon liquid stream respectively. Referring again to the drawing, propane entering the process with the feed in conduit 1 will exit the process in conduit 11, passing to downstream fractionation facilities for recovery. Normal butane entering the process in conduit 1 exits in conduit 13 and passes to downstream treating facilities where trace amounts of organic fluorides and hydrogen fluoride may be removed as desired.

DETAILED DESCRIPTION OF THE INVENTION In the hydrogen fluoride-catalyzed alkylation process of my invention, reactants combine to yield as a principal product a hydrocarbon of carbon content equal to the sum of the carbon atoms of the individual olefin and alkylatable reactants. Such hydrocarbon products are referred to as mono-alkylate since the alkylatable reactant is substituted with only one whole olefinic reactant. Mono-alkylate is the most desirable alkylate product because of its exceptional octane and boiling point characteristics as compared to heavier alkylate, that having a carbon content greater than monoalkylate. This heavier alkylate is a result of undesirable reactions such as polymerization. When alkylation is performed in the presence of hydrogen fluoride, a strongly acidic catalyst, it is necessary to choose reaction conditions which favor alkylation rather than polymerization and other undesirable reactions, since acidic catalysts will also promote the undesirable ones. For simplicity, discussion will be limited to the polymerization reaction. Four major variables are important in minimizing polymerization: reaction temperature, excess of alkylatable reactant, the catalyst and catalyst composition. The process of this invention optimizes these four variables, however, in its essence it most concerns the variable of reaction temperature. Modern designs of alkylation process units include temperature control of the reaction zone. Alkylation reactions are exothermic, and heat must be removed from the reaction zone in order to maintain the temperature at the desired level. Controlling the temperature in the reaction zone would be sufficient, provided that reactions took place only within that zone. However, in these same process units reactions take place outside that zone, and, because the temperature at which those reactions take place is uncontrolled, the temperature can attain levels at which polymerization occurs with resultant detrimental effect upon alkylate quality. When feed to an alkylation process unit comprises isoparaffin and olefin constituents, it is desirable to provide an excess of isoparaffin within the reaction zone by recycling unreacted isoparaffins from the reaction zone effluent back to the fresh feed prior to its introduction to the reaction zone. It is essential that this recycle isoparaffin be thoroughly admixed and intermingled with the olefin-containing fresh feed before contact is effected with the acid catalyst. In conventional units the recycle isoparaffin can contain significant quantities, 2 wt. or more, of hydrogen fluoride. Upon mixing the hydrogen fluoride, recycle isoparaffin and fresh feed, alkylation reactions begin rapidly, and the resulting exothermic heat of reaction raises the temperature of the mixture. When this temperature exceeds F, alkylate quality begins to be adversely affected due to undesirable reactions taking place.

The following example will serve to illustrate the effect upon alkylate product quality of hydrogen fluoride in the recycle isoparaffin. An alkylation process pilot plant was operated in two tests using the same olefinisoparaffin feed and hydrogen fluoride alkylation catalyst. The processing conditions for the two tests were essentially the same except for the hydrogen fluoride content of recycle isoparaffin. The first test (Test 1) approximated the conditions of a commercial plant then in operation, producing 95.2 octane alkylate while having 4.85 wt. hydrogen fluoride in recycle paraffin. In Test 2 the hydrogen fluoride content of recycle isoparaffin was reduced to 0.35 wt.

TEST 1 2 Hydrogen Fluoride in Recycle As shown above, reduction of hydrogen fluoride content in the recycle isoparaffin from 4.85 wt. to 0.35 wt. increased the octane number of the alkylate product from 95.2 to 97.1. The present invention effects this same type of improvement by reducing the hydrogen fluoride content of recycle isoparaffin in a commercial scale plant.

In the embodiment of my invention shown in the attached drawing, 1 1,748 barrels per stream day (BPSD) of olefin-isoparaffin feed enter the process in conduit 1. This feed is of approximately the following composition, expressed in mole percent: propene, 18.6; propane, 1 1.6; butene, 20.3; isobutane, 40.7; normal butane, 8.8. This feed combines with 65,687 BPSD of recycle isoparaffin from conduit 2 of approximately the following composition, expressed in mole percent: propane, 5.2; isobutane, 82.6; normal butane, 8.5; isopentane, 2.1; C and heavier, 1.0; hydrogen fluoride, 0.6. This combined feed and recycle contact hydrogen fluoride in reaction zone 4 and pass to the bottom of mixing-settling zone 6. The mixing-settling zone of this example may be a vertically disposed, cylindrical vessel having a lower mixing section and an upper settling section. The mixing section preferably has flow restrictions placed therein, such as baffles, which maintain the reaction zone effluent in a dispersed state. The volume of the mixing section is selected to provide sufficient residence time for completion of reactions begun in the reaction zone. The settling section of the mixingsettling zone provides for repose of the catalysthydrocarbon dispersion so that phase separation can occur. Catalyst and hydrocarbon phases separate within the settling zone by virtue of their different densities. The settling section of this example may comprise an enclosed void space. The hydrocarbon phase, containing hydrogen fluoride, exits mixing-settling zone 6 in conduit 7 and passes to the rectification zone of my invention. It is well known in theart that rectification is a distillation involving counter current and continuous contact between a vapor and a condensed portion of that vapor. Enrichment of the vapor in the more volatile components is effected. The existence of the condensed portion of the vapor, generally referred to as reflux, makes possible much greater enrichment of the vapor than could be secured by other means such as single distillations using the same amount of heat energy. The rectification zone of my invention makes use of the well known principles of rectification in order to substantially remove hydrogen fluoride from the hydrocarbon phase entering in conduit 7 such that hydrocarbon leaving the lower part of the rectification zone will be substantially hydrogen fluoride-free. The rectification zone of this example may be a conventional rectification tower with 20 or more contact stages; having means for reboiling the bottoms material, partially condensing and separating the condensed overhead materials and returning reflux to the top of the tower' The vapors generated by the reboiler contact reflux on the contact stages to provide the rectification necessary for removal overhead of most of the hydrogen fluoride. Thus, the recycle isoparaffin which mixes with olefinisoparaffin feed before introduction into reaction zone 4 is of such reduced hydrogen fluoride content that no appreciable detriment to the quality of the final alkylate product will result from the undesirable reactions hereinbefore cited. The bottoms product from the rectification zone, comprising alkylate product and unreacted hydrocarbons exits rectification zone 8 in conduit 9 and passes to separation zone 10'. 8,058 BPSD of alkylate product exit separation zone 10 in conduit 14. 4.266 BPSD of hydrocarbon liquid exit separation zone 10 in conduit 13 and pass to downstream treating facilities. This hydrocarbon liquid is of approximately the following composition, expressed in mole percent: isobutane, 5.1; normal butane, 91.8; isopentane, 2.1; hexane and heavier, 1.0.

My invention is not restricted to the conditions of the aforementioned example. A suitable alkylatable reactant may be a paraffinic hydrocarbon having a tertiary carbon atom, such as 2-methylbutane, 2- methylpentane, etc. Other useful alkylatable reactants include benzene, toluene, xylene, naphthenes, phenols, cresols, amines and the like. The olefin reactants which suitably may be used in my invention include C -C olefinic hydrocarbons, alkyl halides, alcohols, alkyl sulfates, alkyl phosphates, etc. Hydrogen fluoride is used as the alkylation catalyst. A preferred hydrogen fluoride catalyst contains from -90% hydrogen fluoride with less than 2% water. Alkylation reaction conditions to be maintained within the reaction zone include a temperature from about 0 to about 150F, and a pressure of about 1 atmosphere to about 40 atmospheres. A preferred range of temperature is from about 30 to about F. Pressure is not a significant variable with respect to product quality, provided that it is sufficient to keep all hydrocarbon in the liquid state. The volumetric ratio of acid catalyst to hydrocarbon within the reaction zone is maintained within the range of 1:1 to 2:1. At some point below 0.8:1 excess polymer forms which contaminates the alkylate product. There appears to be no alkylate yield or quality improvement in increasing this ratio above 2:1. The contact time in the alkylation reaction zone is typically less than 5 minutes and preferably from about 10 to about 60 seconds. It is desirable to maintain a high mole ratio of paraffin or aromatic present to the olefin present in order to produce high quality monoalkylate. A broad range of this ratio is from about 7:1 to about 20:1 with a preferred operating range being from about 8:1 to 16: 1. The residence time in the mixing-settling zone is preferably from about 100 seconds to about 1200 seconds. Operating conditions in the rectification zone are selected, according to the type of reactants being charged to the process, to maintain lower section products essentially free of hydrogen fluoride.

Another utility of the rectification zone of my invention is in increasing the capacity of an existing hydrogen fluoride-catalyzed alkylation process unit. It has happened that by the time a new alkylation unit is completed the demand for its product has grown to such an extent that provision of more processing capacity would be highly advantageous. Capacity can be increased with relatively little expense on a given plant until reaching the point of overloading of some large piece of equipment. In hydrogen fluoride catalyzed alkylation units this piece is generally found to be the separation zone. In these cases large increases in capacity can be realized, as well as an increase in product quality, by the installation of a rectification zone. In conventional designs the hydrocarbon phase effluent from the mixing-settling zone passes directly to the separation zone. Referring again to the attached drawing, without the inclusion of the rectification zone the hydrocarbon effluent from the mixing-settling zone 6 which exits in conduit 7 would pass directly to separation zone 10'. In such case not only would the separation zone have to pass overhead recycle isoparaffins but also the liquefied hydrocarbon vapor and the hydrogen fluoride stream shown as the streams in conduits 11 and 10, respectively. Feed to the separation zone, in the process of my example without a rectification zone, amounts to 617,069 pounds per hour of material. With inclusion of the rectification zone this feed rate decreases to 432,722 pounds per hour, a 30% decrease in the loading of the separation zone. This means that if an alkylation unit were pushed to the limit of capacity and the separation zone were limiting at that rate, the inclusion of a rectification zone in the process would allow the unit capacity to be increased even more, as well as improving the quality of the alkylate product.

I claim as my invention:

1. An alkylation process which comprises the steps a. reacting an isoparaffin with an olefin in contact with hydrogen fluoride catalyst at alkylation conditions in a reaction zone;

b. separating the reaction zone effluent into a hydrogen fluoride phase and a hydrocarbon phase containing hydrogen fluoride;

c. returning at least a portion of the hydrogen fluoride phase to said reaction zone;

d. passing said hydrocarbon phase to a rectification zone to separate therefrom a hydrogen fluoride stream, an isoparaffin stream and an alkylate stream containing additional unreacted isoparaffin;

e. recycling said hydrogen fluoride stream and said isoparaffin stream to said reaction zone;

f. fractionating said alkylate stream to separate unreacted isoparaffin therefrom and recycling said unreacted isoparaffin to said reaction zone; and

g. recovering the alkylate product from fractionating step (f).

2. A process for producing high-octane alkylated hydrocarbons which comprises the steps of:

a. introducing an isoparaffin-olefin feed into a reaction zone;

b. contacting said feed with hydrogen fluoride alkylation catalyst in said reaction zone at alkylation reaction conditions;

c. passing a reaction zone effluent comprising hydrogen fluoride, alkylated hydrocarbons and unreacted hydrocarbons into a lower portion of a vertical mixer-settler for passage of said effluent upwardly therethrough, said mixer-settler having a lower mixing section and an upper settling section;

d. passing said reaction zone effluent upwardly through said lower mixing section and maintaining said effluent in said mixing section of said mixersettler for a time sufficient to complete the alkylation reaction;

e. withdrawing a hydrocarbon phase containing hydrogen fluoride from an upper portion of said settling section, and recycling a hydrogen fluoride phase from a lower portion of said settling section to said reaction zone;

f. passing said hydrogen fluoride-containing hydrocarbon phase to a rectification zone operated under conditions selected to separate (1) a hydrocarbon liquid of reduced hydrogen fluoride content comprising alkylated hydrocarbons, normal paraffin and unreacted isoparaffin, (2) an isoparaffin liquid stream, (3) lower-boiling hydrocarbon vapor stream and (4) a liquid hydrogen fluoride stream;

g. returning said liquid hydrogen fluoride stream to said reaction zone;

h. passing said hydrocarbon liquid from step (f) into a fractionation zone to separate (1) high-octane alkylated hydrocarbons as product of said process, (2) a normal paraffin liquid and (3) unreacted isoparaffin, and

i. returning said isoparaffin stream from step (f) and said unreacted isoparaffin from step (h) to said olefin-isoparaffin feed of step (a) prior to the introduction of said feed into said reaction zone.

3. The process of claim 2 further characterized in that said isoparaffin-olefin feed comprises isobutane and an olefin having 3 or 4 carbon atoms per molecule.

4. The process of claim 2 further characterized in that said isoparaffin-olefin feed comprises isobutane and butylene.

5. The process of claim 2 further characterized in that said hydrogen fluoride alkylation catalyst is maintained between about and weight percent hydrogen fluoride.

6. The process of claim 5 further characterized in that said lower-boiling hydrocarbon vapor stream comprises hydrocarbon molecules having less than 5 and more than 2 carbon atoms.

7. The process of claim 5 further characterized in that the mole ratio of isobutane to olefin in said isoparaffin-olefin feed is maintained above 7:1.

8. The process of claim 5 further characterized in that said normal paraffin liquid comprises butane. 

1. AN ALKYLATION PROCESS WHICH COMPRISES THE STEPS OF: A. REACTING AN ISOPARAFFIN WITH AN OLEFIN IN CONTACT WITH HYDROGEN FLUORIE CATALYST AT ALKYLATION CONDITIONS IN A REACTION ZONE, B. SEPARATING THE REACTION ZONE EFFUENT INTO A HYDROGEN FLUORIDE PHASE AND A HYDROCARBON PHASE CONTAINING HYDROGEN FLUORIDE, C. RETURNING AT LEAST A PORTION OF THE HYDROGEN FLUORIDE PHASE TO SAID REACTION ZONE, D. PASSING SAID HYDROCARBON PHASE TO A RECTIFICATION ZONE TO SEPARATE THEREFROM A HYDROGEN FLUORIDE STREAM, AN ISOPARAFFIN STREAM AND AN ALKYLATE STREAM CONTAINING ADDITIONAL UNREACTED ISOPARAFIN, E. RECYCLING SAID HYDROGEN FLUORIDE STREAM AND SAID ISOPARAFFIN STREAM TO SAID REACTION ZONE, F. FRACTIONATING SAID ALKYLATE STREAM TO SEPARATE UNREACTED ISOPARAFFIN THEREFROM AND RECYCLING SAID UNREACTED ISOPARAFFIN TO SAID REACTION ZONE, AND G. RECOVERING THE ALKYLATE PRODUCT FROM FRACTIONATING STEP (F).
 2. A process for producing high-octane alkylated hydrocarbons which comprises the steps of: a. introducing an isoparaffin-olefin feed into a reaction zone; b. contacting said feed with hydrogen fluoride alkylation catalyst in said reaction zone at alkylation reaction conditions; c. passing a reaction zone effluent comprising hydrogen fluoride, alkylated hydrocarbons and unreacted hydrocarbons into a lower portion of a vertical mixer-settler for passage of said effluent upwardly therethrough, said mixer-settler having a lower mixing section and an upper settling section; d. passing said reaction zone effluent upwardly through said lower mixing section and maintaining said effluent in said mixing section of said mixer-settler for a time sufficient to complete the alkylation reaction; e. withdrawing a hydrocarbon phase containing hydrogen fluoride from an upper portion of said settling section, and recycling a hydrogen fluoride phase from a lower portion of said settling section to said reaction zone; f. passing said hydrogen fluoride-containing hydrocarbon phase to a rectification zone operated under conditions selected to separate (1) a hydrocarbon liquid of reduced hydrogen fluoride content comprising alkylated hydrocarbons, normal paraffin and unreacted isoparaffin, (2) an isoparaffin liquid stream, (3) lower-boiling hydrocarbon vapor stream and (4) a liquid hydrogen fluoride stream; g. returning said liquid hydrogen fluoride stream to said reaction zone; h. passing said hydrocarbon liquid from step (f) into a fractionation zone to separate (1) high-octane alkylated hydrocarbons as product of said process, (2) a normal paraffin liquid and (3) unreacted isoparaffin, and i. returning said isoparaffin stream from step (f) and said unreacted isoparaffin from step (h) to said olefin-isoparaffin feed of step (a) prior to the introduction of said feed into said reaction zone.
 3. The process of claim 2 further characterized in that said isoparaffin-olefin feed comprises isobutane and an olefin having 3 or 4 carbon atoms per molecule.
 4. The process of claim 2 further characterized in that said isoparaffin-olefin feed comprises isobutane and butylene.
 5. The process of claim 2 further characterized in that said hydrogen fluoride alkylation catalyst is maintained between about 80 and 90 weight percent hydrogen fluoride.
 6. The process of claim 5 further characterized in that said lower-boiling hydrocarbon vapor stream comprises hydrocarbon molecules having less than 5 and more than 2 carbon atoms.
 7. The process of claim 5 further characterized in that the mole ratio of isobutane to olefin in said isoparaffin-olefin feed is maintained above 7:1.
 8. The process of claim 5 further characterized in that said normal paraffin liquid comprises butane. 